In digital mammography (DM), a single image or several images of a body part, such as a breast, of a patient are taken at different angles using a high energy electromagnetic x-ray source and a single layer flat panel x-ray detector. These images are then used for the diagnosis or treatment of breast cancer or other disease.
Digital subtraction mammography (DSM) is a method of breast angiography wherein a contrast media is intravenously injected into a patient to enhance the acquired image. This method is used to visualize cancers that cannot be seen using standard DM, for example in breasts having a high density. It is also thought that using DSM enhances the visualization of calcifications and help in the monitoring and treatment of breast cancer.
During the development of cancer, the growth of new blood vessels occurs which is also known as tumor angiogenesis. With an increase in tumor cell population, new capillary growth accompanies an increase in tumor cell population to provide sufficient materials for cell proliferation. This property is used by DSM since cancers will absorb the contrast agent more quickly than other tissues and masses. The resulting image thus enhances the area of lesions and removes the contrast due to normal tissue.
Two known methods for carrying out DSM are temporal subtraction and dual energy subtraction. Both of these methods can be carried out in DM units.
For the temporal subtraction method, an image of the breast is acquired before the administration of an iodinated contrast agent. This image is known as a pre-contrast image. A contrast agent, for example the iodinated contrast agent, is then intravenously injected into the patient and then a second image is taken. This image is known as the post-contrast image. Software is then used to subtract the pre-contrast image from the post-contrast image with the result being an image where the material in the breast that contains the contrast agent is enhanced. In this procedure, two separate images are taken which means that a patient is exposed to two doses of x-rays.
For the dual energy subtraction method, the pre-contrast image is eliminated and instead two images are taken after the injection of the contrast agent, each image at a different energy and a different instant in time thereby exposing a patient to two doses of X-rays. The two images are taken within typically a fraction of a second from each other after the injection of the contrast agent. One of the images is taken with an x-ray beam having a narrow x-ray energy spectrum centered below the K-edge of the contrast agent and is typically known as the low-energy image. The other image is taken with an x-ray beam having a narrow x-ray energy spectrum centered above the K-edge of the contrast agent and is typically known as the high-energy image. Software is used to subtract the low-energy image from the high-energy image to obtain an image where the material in the breast which contains the contrast agent is enhanced.
Although the effect of the patient's motion is reduced for the dual energy subtraction method compared to the temporal subtraction method, alignment issues of the two images are still existent, for example due to cardiac, respiratory, or patient movement. As previously mentioned, for dual energy subtraction, the low-energy and high-energy images are taken typically within a fraction of a second from each other. Therefore, it would be desirable to have a method for reducing misalignment issues.
Therefore, it is desirable to provide a multi-layer flat panel X-ray detector which allows for two images to be obtained using one x-ray dose.